Darwin extern/static fix

Bugzilla #1576 and the fix committed for it is only partially right. 
The patch applewmExt.h is right, but patching the imported Mesa code 
in extras/Mesa/include/GL/internal/dri_interface.h is the wrong thing 
to do and likely has unintended side effects on other platforms. The 
correct fix is just to rename __driConfigOptions in 
lib/GL/apple/dri_glx.c. Thanks for pointing out the issue.

--Torrey

P.S. The problem with __driConfigOptions is exactly why it makes some 
sense to have mixed extern/static definitions. Static is supposed to 
override any external definitions inside the file to eliminate future 
namespace collision problems. __driConfigOptions was defined inside 
lib/GL/apple/dri_glx.c for awhile before Mesa added an identically 
named extern symbol.